Since then, the tiny pest had appeared to remain in Berkshire County, where it was discovered in a trap in Dalton, a small town near Pittsfield.

The discovery last month that the beetle is elsewhere in the state — it has been moving eastward since it was first found in the United States near Detroit in 2002 — did not surprise state officials and arborists. But they called the spread potentially ominous for the state’s estimated 45 million ash trees, which represent about 3 percent of the state’s trees.

“It’s very concerning,” said Ken Gooch, director of the Forest Health Program at the state Department of Conservation and Recreation. “You just don’t want to see it. It affects all the ash trees. We were hoping to keep it contained for as long as possible in the Berkshires.”

Gooch said his agency received reports earlier this fall of the so-called blonding of ash trees on the Osgood Hill property in North Andover, which is owned by the town. The blonding, or denuding of the trees, came from woodpeckers pulling off chunks of bark to get at the larvae infesting the trees.

When he went to investigate Nov. 20, Gooch found an alarming number of larvae in more than a dozen trees on the preserve. He found them lower than he would have liked on the trees, suggesting they had been there for years.

Gooch said the state is seeking permission from town officials to take down many of the infested trees, and expects, at a minimum, that the state will quarantine all ash wood in Essex County. He said the state may restrict the movement of all species of firewood as well as logs, stumps, branches, and other forms of ash wood.

Town officials said they are awaiting direction from the state. “It’s something everyone should be concerned about,” said Jennifer Hughes, the town’s conservation administrator.

Gooch said it is unclear how the insects moved so far across the state, without being found in between. He said they most likely hitched a ride on firewood or other ashes brought to the area, as the insects do not move far on their own.

The emerald-colored beetles are native to Asia and often kill ash trees within a few years, as their larvae bore under the bark and interfere with a tree’s circulatory system. They can cause major damage before anyone notices, as they scavenge mainly on the tops of trees.

Their spread has been compared with the 2008 infestation of Asian longhorned beetles in Worcester, where about 30,000 trees have been uprooted.

David R. Foster, director of the Harvard Forest in Petersham, called the spread of the beetles “really troubling,” especially for the greater number of ash trees in New Hampshire, Maine, and Vermont.

He noted how ash wood is a commodity used for everything from baseball bats to furniture.

“We’re essentially helpless against their spread,” Foster said. “Most of us expect that ash will essentially be eliminated as a species here.”